The present invention relates to a vortex gasket to be placed between flange faces having conical surfaces, in a flange joint structure of automotive exhaust systems.
Generally, in a flange joint structure of automotive exhaust system, a flat grooved flange, orthogonal to the tube axial line, is tightened, with a vortex gasket placed in the groove thereof, but this flat flange is manufactured separately from the exhaust manifold, and other elements, and welded thereon later, which causes problems in weight and manufacturing cost.
Recently, therefore, in automotive exhaust systems, by bulging tubes at or near ends thereof, flanges have been integrally formed, and it has been attempted to reduce the weight of the exhaust systems while reducing manufacturing costs. In such a flange (hereinafter called a special flange), the seal surface, as the crimping surface of the seal member, is not a flat surface orthogonal to the tube axial line, as in the case of the above flat plate flange, but forms a conical shape, inclined to the tube axial line.
Incidentally, a traditional vortex gasket is formed by integrally overlaying spirally a metal hoop, whose sectional shape in width has a waveform, and an inorganic filler in a tape form. Such a gasket excels in the property of compressibility and recovery, among other things, because of the presence of the metal hoop, and is ideal as the seal between flanges; but, structurally, it cannot be used in the special flange as mentioned above. More specifically, this vortex gasket has the overlaid annular layers of hoop and filler engaged with each other in waveform, and is extremely high in rigidity against deformation in an axial direction; hence it is not easy to deform gasket end surfaces (or side surfaces) contacting flange seal surfaces (hereinafter called seal face contact surfaces) from a flat state, orthogonal in the axial direction. Therefore, when placed between the special flanges, the seal face contact surfaces cannot be deformed in a conical shape corresponding to the flange seal surfaces, and if an attempt is made to deform by force, abnormal deformation or gaps may be caused around the filler, so that further favorable seal function cannot be exhibited. Of course, if such a vortex gasket were fabricated and formed preliminarily in a shape corresponding to the seal surface shape, occurrence of such abnormal deformation and gaps cannot be avoided, and favorable seal function cannot be obtained. If follows from these points, that the traditional vortex gasket cannot be used, by any means, with the special flanges having a conical seal surfaces.
It may be considered to use something that can be easily deformed and formed into a shape corresponding to the seal surface of the seal face contact surface as the seal member to be placed between such special flanges. For example, a graphite material covered with metal mesh and pressed and formed into a desired shape could be used, but such a seal member is inferior to a vortex gasket, as a matter of course, in properties of compressibility and recovery, among others, so that a tightening surface pressure cannot be raised. Further, it may be broken upon removal after use. Or, it is higher in cost, and hence not practical.
It is hence a primary object of the invention to provide a vortex gasket maintaining intrinsic excellent functions for providing a seal between flanges, preferably being usable in special flanges having a conical seal surface and being applicable, following recent trends, for special flanges in automotive exhaust systems.